Impaired immune function in patients with xeroderma pigmentosum.

The development of contact allergy in sun-exposed skin is markedly impaired in patients with xeroderma pigmentosum as compared to the responses in healthy control subjects. The degree of this immunological impairment is directly related to the severity of the cutaneous disease. These findings raise the possibility that sunlight-induced alterations of immune function may be involved in the marked susceptibility of these patients to the development of nonmelanoma skin cancer.